Generally, crystalline N,N-dialkylglycine is produced through synthesis of an alkali metal salt of the N,N-dialkylglycine. However, the N,N-dialkylglycine alkali metal salt has a low solubility in water. For example, N,N-dimethylglycine sodium salt has a water solubility of 25% by mass (20° C.): a higher concentration of the aqueous N,N-dimethylglycine alkali metal salt solution is not achievable. Since the aqueous N,N-dialkylglycine alkali metal salt solution cannot be prepared in a higher concentration, a storage tank for storing the aqueous solution should be larger and the expense for transportation is higher, resulting inevitably in a higher cost.
On the other hand, the preparation process of an aqueous N,N-dialkylglycine solution by dissolving crystalline N,N-dialkylglycine has disadvantages of a higher cost and much labor in crystallization and handling of the N,N-dialkylglycine. For example, the crystalline N,N-dimethylglycine can be prepared through complicated procedures including organic solvent extraction and crystallization as disclosed in U.S. Pat. No. 4,968,839. Further, the obtained N,N-dimethylglycine is extremely hygroscopic, requiring low humidity for the treatment and storage thereof, and rendering its handling more difficult.
The inventors of the present invention, after comprehensive study to solve the above problems, found that N,N-dialkylglycines have a much higher solubility in water in comparison with N,N-dialkylglycine alkali metal salts having a low solubility in water, and have completed the present invention of the aqueous high-concentration N,N-dialkylglycine solution and the process for production thereof.
The present invention intends to provide an aqueous high-concentration N,N-dialkylglycine solution which is readily handleable and economical in storage, transportation, and so forth, and is useful as a source material solution for organic chemical reactions. The present invention intends also to provide a process for production thereof.